Hi Simon and Travis,
Thanks for the explanations. I am not sure if there are that many
additional use cases, but a meta meta class sounds reasonable to me:) As
always the main problem is finding the right place to look in the
documentation - or the right person to explain it to you.
Thanks again,
Andrew
On Thursday, 17 March 2016 01:10:44 UTC+11, Simon King wrote:
>
> Hi Andrew,
>
> On 2016-03-16, Andrew wrote:
> > I want this functionality too. I tried adding:
> >
> > __metaclass__ = ClasscallMetaclass
> >
> > but this produces the error:
> >
> > TypeError: Error when calling the metaclass bases
> > metaclass conflict: the metaclass of a derived class must be a (non-
> > strict) subclass of the metaclasses of all its bases
>
> That's a general problem. The point is: If a class C with a meta-class M
> has several base classes B1,...,Bn with meta-classes M1,...,Mn, then
> Python will give you that error unless one of the meta-classes is
> a sub-class of all other meta-classes.
>
> By consequence, if we want to combine the features provided by the
> meta-classes M, M1, M2,... then we need to explicitly create another
> meta-class Mx that combines the features from the other meta-classes.
> And then you have to explicitly invoke Mx for C, rather than just inherit
> it from M and the meta-classes of C's base classes.
>
> I once tried to solve that problem, by introducing a meta-meta-class MM.
> I.e., each meta-class M, M1, M2,... in Sage would be instance of MM, and
> when you try to combine their features, then MM would create a common
> sub-meta-class Mx of M, M1, M2, ... on the fly (i.e., what we now have
> to do manually would become automatic).
>
> It did work. But I guess that idea is just too confusing and the use
> cases (at that time) have been too few. Perhaps there are more use cases
> now?
>
> Best regards,
> Simon
>
>
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